Microelectromechanical sensor with improved mechanical decoupling of sensing and driving modes

ABSTRACT

A driving mass of an integrated microelectromechanical structure is moved with a rotary motion about an axis of rotation, and a sensing mass is connected to the driving mass via elastic supporting elements so as to perform a detection movement in the presence of an external stress. The driving mass is anchored to a first anchorage arranged along the axis of rotation by first elastic anchorage elements. The driving mass is also coupled to a pair of further anchorages positioned externally thereof and coupled to opposite sides with respect to the first anchorage by further elastic anchorage elements; the elastic supporting elements and the first and further elastic anchorage elements render the driving mass fixed to the first sensing mass in the rotary motion, and substantially decoupled from the sensing mass in the detection movement, the detection movement being a rotation about an axis lying in a plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

More than one reissue application has been filed for the reissue of U.S.patent application Ser. No. 12/208,980, filed Sep. 11, 2008, whichissued as U.S. Pat. No. 8,042,396. The reissue applications areapplication Ser. No. 14/062,671 (the present application), filed on Oct.24, 2013 and Ser. No. 14/871,240, filed on Sep. 30, 2015, both of whichare reissues of U.S. patent application Ser. No. 12/208,980, filed Sep.11, 2008.

BACKGROUND

1. Technical Field

The present invention relates to a microelectromechanical sensor havingimproved mechanical decoupling of sensing and driving modes. Inparticular, in the following description reference will be made to agyroscope (whether uniaxial, biaxial or triaxial), which can possiblyoperate as an accelerometer (whether uniaxial, biaxial or triaxial).

2. Description of the Related Art

As is known, microprocessing techniques enable formation ofmicroelectromechanical structures or systems (the so-called MEMS) withinlayers of semiconductor material, which have been deposited (forexample, in the case of a layer of polycrystalline silicon) or grown(for example, in the case of an epitaxial layer) on top of sacrificiallayers, which are removed by chemical etching. Inertial sensors,accelerometers and gyroscopes obtained with this technology areencountering an increasing success, for example in the automotive field,in inertial navigation, or in portable devices.

In particular, integrated semiconductor gyroscopes are known, which aremade with MEMS technology. Gyroscopes operate according to the theoremof relative accelerations, exploiting Coriolis acceleration. When anangular velocity is imparted on a movable mass that is moving with alinear velocity, the movable mass “feels” an apparent force, referred toas Coriolis force, which causes a displacement thereof in a directionperpendicular to the direction of the linear velocity and to the axis ofrotation. The movable mass is supported via springs that enable adisplacement in the direction of the apparent force. According toHooke's law, the displacement is proportional to the apparent force, andconsequently, based on the displacement of the movable mass, it ispossible to detect the Coriolis force and the angular velocity that hasgenerated it. The displacement of the movable mass can, for example, bedetected capacitively, by measuring, in resonance conditions, thecapacitance variations caused by the movement of movable electrodes,integrally fixed to the movable mass and operatively coupled to fixedelectrodes.

US2007/214883, assigned to STMicroelectronics Srl, discloses amicroelectromechanical integrated sensor with a rotary driving motion,which is sensitive to pitch and roll angular velocities.

This microelectromechanical sensor includes a single driving mass,anchored to a support at a single central point and driven with rotarymotion about an axis, which passes through the central point and isorthogonal to the plane of the driving mass. The rotation of the drivingmass enables two mutually orthogonal components of driving velocity inthe plane of the mass. At least one through opening is provided insidethe driving mass, in which a sensing mass is arranged; the sensing massis enclosed within the driving mass, suspended with respect to thesubstrate, and connected to the driving mass via flexible elements. Thesensing mass is fixed to the driving mass during its rotary motion, andhas a further degree of freedom of movement as a function of an externalstress, in particular a Coriolis force acting on the sensor. Theflexible elements, according to their particular construction, allow thesensing mass to perform a rotary movement of detection about an axislying in the plane of the sensor in response to a Coriolis accelerationacting in a direction perpendicular to the plane, in a way substantiallydecoupled from the driving mass. The microelectromechanical structure,in addition to being compact (in so far as it envisages just one drivingmass that encloses in its overall dimensions one or more sensingmasses), enables with minor structural modifications, a uniaxial,biaxial or triaxial gyroscope (and/or an accelerometer, according to theelectrical connections implemented) to be obtained, at the same timeensuring decoupling of the driving mass from the sensing mass during themovement of detection.

In detail, and as shown in FIG. 1, that relates to a uniaxial sensor,the microelectromechanical sensor, denoted with 1, comprises a drivingstructure formed by a driving mass 3 and by a driving assembly 4. Thedriving mass 3 has a circular geometry with radial symmetry, with asubstantially planar configuration having a main extension in a planedefined by a first axis x and by a second axis y (referred to in whatfollows as “plane of the sensor xy”), and negligible dimension, withrespect to the main extension, in a direction parallel to a third axis(referred to in what follows as “orthogonal axis z”), forming with thefirst and second axes x, y a set of three orthogonal axes fixed withrespect to the sensor structure. In particular, the driving mass 3 hasin the plane of the sensor xy substantially the shape of an annulus, anddefines at the center a circular empty space 6, the center O of whichcoincides with the centroid and the center of symmetry of the drivingmass 3. The driving mass 3 is anchored to a substrate 2 by means of acentral anchorage 7 arranged at the center O, to which it is connectedthrough elastic anchorage elements 8. For example, the elastic anchorageelements 8 depart in a crosswise configuration from the center O along afirst axis of symmetry A and a second axis of symmetry B of the drivingmass 3, the axes of symmetry being parallel, respectively, to the firstaxis x and to the second axis y. The elastic anchorage elements 8 enablea rotary movement of the driving mass 3 about a drive axis passingthrough the center O, parallel to the orthogonal axis z andperpendicular to the plane of the sensor xy.

The driving mass 3 has a first pair of through-openings 9a, 9b with asubstantially rectangular shape elongated in a direction parallel to thesecond axis y, aligned in a diametric direction along the first axis ofsymmetry A, and set on opposite sides with respect to the empty space 6.In particular, the direction of alignment of the through-openings 9a, 9bcorresponds to a direction of detection of the microelectromechanicalsensor 1 (in the case represented in the figure, coinciding with thefirst axis x).

The driving assembly 4 comprises a plurality of driven arms 10 (forexample, eight in number), extending externally from the driving mass 3in a radial direction and spaced apart at a same angular distance, and aplurality of first and second driving arms 12a, 12b, extending parallelto, and on opposite sides of, respective driven arms 10 and anchored tothe substrate via respective anchorages. Each driven arm 10 carries aplurality of first electrodes 13, extending in a direction perpendicularto, and on either side of, the driven arm. Furthermore, each of thefirst and second driving arms 12a, 12b carries respective secondelectrodes 14a, 14b, extending towards the respective driven arm 10 andcomb-fingered to the corresponding first electrodes 13. The firstdriving arms 12a are all arranged on the same side of the respectivedriven arms 10 and are all biased at a first voltage. Likewise, thesecond driving arms 12b are all arranged on the opposite side of therespective driven arms 10, and are all biased at a second voltage. In aper se known manner which is not described in detail, a driving circuitis connected to the second electrodes 14a, 14b so as to apply the firstand second voltages and determine, by means of mutual and alternatingattraction of the electrodes, an oscillatory rotary motion of thedriving mass 3 about the drive axis, at a given oscillation frequency.

The microelectromechanical sensor 1 further comprises a first pair ofacceleration sensors with axis parallel to the orthogonal axis z, and inparticular a first pair of first sensing masses 16a, 16b, eachpositioned in a respective one of the through-openings 9a, 9b, so as tobe completely enclosed and contained within the overall dimensions ofthe driving mass 3 in the plane of the sensor xy. The first sensingmasses 16a, 16b have a generally rectangular shape matching the shape ofthe respective through opening 9a, 9b, and are formed by a firstrectangular portion 17, which is wider, and by a second rectangularportion 18, which is narrower (along the first axis x), connected by aconnecting portion 19, which is shorter (in a direction parallel to thesecond axis y) than the first and second rectangular portions. Eachfirst sensing mass 16a, 16b has a centroid G located within thecorresponding first rectangular portion 17, and is supported by a pairof elastic supporting elements 20. The elastic supporting elements 20are connected to the connecting portion 19, and extend towards thedriving mass 3, in a direction parallel to the second axis y. In otherwords, the elastic supporting elements 20 extend within recesses 21provided at opposite sides of the sensing masses 16a, 16b. The elasticsupporting elements 20 extend at a distance from the centroid G of therespective first sensing mass 16a, 16b, and form torsional springs thatare rigid for the rotary motion of the driving mass 3, and also enablerotation of the sensing masses about an axis of rotation parallel to thesecond axis y and lying in the plane of the sensor xy (and,consequently, their movement out of the plane of the sensor xy).

A pair of first and second detection electrodes 22, 23 is arrangedunderneath the first and second rectangular portions 17, 18 of each oneof the first sensing masses 16a-16b; for example the detectionelectrodes 22, 23 are constituted by regions of polycrystalline siliconformed on the substrate 2, having equal dimensions substantiallycorresponding to those of the second (and smaller) rectangular portion18. The first and second detection electrodes 22, 23 are separated,respectively from the first and second rectangular portions 17, 18, byan air gap, and are connected to a read circuit. The first and seconddetection electrodes 22, 23 hence form, together with the first andsecond rectangular portions 17, 18 respective detection capacitors.

In use, the microelectromechanical sensor 1 is able to operate as agyroscope, designed to detect an angular velocity {right arrow over(Ω)}_(x) (in FIG. 1 assumed as being counterclockwise), about the firstaxis x.

On the hypothesis of small displacements of the first sensing masses16a-16b and of small rotations of the driving mass 3, the rotarymovement of the driving mass 3 and of the first sensing masses 16a-16babout the drive axis can be represented by a driving-velocity vector{right arrow over (v)}_(a), tangential to the circumference thatdescribes the driving trajectory.

In particular, the rotary motion about the first axis x at the angularvelocity {right arrow over (Ω)}_(x) determines a force acting on theentire structure, known as Coriolis force (designated by {right arrowover (F)}_(c)). In particular, the Coriolis force {right arrow over(F)}_(c) is proportional to the vector product between the angularvelocity {right arrow over (Ω)}_(x) and the driving velocity {rightarrow over (v)}_(a), and is hence directed along the orthogonal axis z,is zero in the points where the driving velocity {right arrow over(v)}_(a) is parallel to the first axis x, and, in the points where itdoes not go to zero, it is directly proportional to the driving velocity{right arrow over (v)}_(a), and consequently it increases with thedistance from the center O. Over the entire structure, considered as asingle rigid body, it is hence possible to identify a distribution ofCoriolis forces that vary as the distance from the center O varies. Theresultants of the Coriolis forces {right arrow over (F)}_(c) acting onthe first sensing masses 16a, 16b at the corresponding centroid G, causerotation of the sensing masses, which move out of the plane of thesensor xy, about an axis parallel to the second axis y and passingthrough the first elastic supporting elements 20. This movement isallowed by the torsion of the first elastic supporting elements 20.Instead, the configuration of the elastic anchorage elements 8 is suchas to inhibit, at least to a first approximation (see the followingdiscussion), movement of the driving mass 3 out of the plane of thesensor xy, thus allowing decoupling of the motion of detection of thefirst sensing masses from the driving motion. The displacement of thefirst sensing masses 16a, 16b out of the plane of the sensor xy causes adifferential capacitive variation of the detection capacitors, the valueof which is proportional to the angular velocity {right arrow over(Ω)}_(x), which can hence be determined in a per-se known manner via apurposely provided read circuit. In particular, since the reading schemeis differential, the presence of a pair of first sensing masses enablesautomatic rejection of spurious linear accelerations along theorthogonal axis z. These accelerations, in fact, cause a variation inthe same direction of the detection capacitors, which is cancelled bythe differential reading (on the contrary, the same structure can beoperated as an accelerometer for detecting the accelerations along theorthogonal axis z, simply by modifying the electrical connectionsbetween the sensing masses and electrodes). The presence of the centralanchorage also enables rejection of spurious linear accelerations alongthe axes x and y, given that the arrangement of elastic anchorageelements 8 is extremely rigid in these directions, and does not enabledisplacement of the sensing masses. Furthermore, the described structureis able to mechanically reject spurious angular acceleration about theorthogonal axis z, since the frequency response of the sensor can bemodeled as a very selective filter.

Although it is advantageous with respect to traditional gyroscopestructures, the Applicant has realized that the describedmicroelectromechanical sensor is not optimized, in particular withrespect to the decoupling between the driving and sensing modes ofoperation.

In detail, the Applicant has realized that flaws in the manufacturingprocess or improper choices in the structure geometry (e.g. a thicknesstoo small with respect to the dimensions in the plane of the sensor xy,or an improper shape of the elastic elements) may result in themicroelectromechanical structure having an improper ratio between thestiffness in the orthogonal direction z and the stiffness in the planeof the sensor xy. In particular, the driving mass 3 could have aninsufficient stiffness in the orthogonal direction z, so thatapplication of the Coriolis force F_(c) would lead to oscillationsmovement outside of the plane of the sensor xy not only by the sensingmasses (as desired) but also by the same driving mass (contrary to theexpected operation). In other words, the decoupling between the drivingand sensing movements could be impaired.

FIG. 2 shows a situation in which the stiffness of the structure in theorthogonal direction z (provided by the elastic anchorage elements 8connecting the driving mass 3 to the central anchorage 7) is notsufficient to avoid undesired movements of the driving mass 3 outsidethe plane of the sensor xy, following application of the Coriolis forceF_(c).

The lack of a perfect decoupling between the driving and sensingmovements entails a number of disadvantages in themicroelectromechanical sensor.

Firstly, any non-ideality in the driving arrangement affects also thesensing arrangement, and vice versa.

Secondly, during sensing operations, the driving movement is altered,mainly due to the variation in the facing area of the driving electrodes(first electrodes 13 and corresponding second electrodes 14a, 14b),because of the movement of the driving mass 3 outside of the plane ofthe sensor xy. Indeed, the Coriolis force F_(c) is a function of thetangential driving velocity {right arrow over (v)}_(a), according to theexpression:

$F_{c} = {{2 \cdot m \cdot \overset{->}{\Omega}} \times {\overset{->}{v}}_{a}}$wherein m is the mass of the sensing mass, {right arrow over (Ω)} is theangular velocity that is to be detected (e.g. the angular velocity{right arrow over (Ω)}_(x)) and {right arrow over (v)}_(a) is thedriving velocity at the application point of the Coriolis force F_(c). Avariation of the driving velocity {right arrow over (v)}_(a) due to adifferent facing area between the electrodes causes a correspondingvariation of the Coriolis force F_(c) and a variation in the output gainof the sensor. As a result, an undesired variation of the overallsensitivity of the microelectromechanical sensor 1 may occur.

Finally, a structure that is compliant (to a certain degree) outside theplane of the sensor xy is inevitably more affected to shock directedalong the orthogonal direction z.

BRIEF SUMMARY

One embodiment of the present invention provides an integratedmicroelectromechanical structure that allows the aforesaid problems anddisadvantages to be overcome, and in particular that has an improvedmechanical decoupling between driving and sensing modes.

According to one embodiment of the present invention, an integratedmicroelectromechanical structure is consequently provided as defined inthe present disclosure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present invention, preferredembodiments thereof are now described purely by way of non-limitingexamples and with reference to the attached drawings, wherein:

FIG. 1 is a schematic top plan view of a microelectromechanicalstructure of a known type;

FIG. 2 is a schematic lateral section of the structure of FIG. 1, duringa sensing operating mode;

FIG. 3 is a schematic top plan view of a microelectromechanicalstructure according to one embodiment of the present invention;

FIG. 4 is a schematic lateral section of the structure of FIG. 3, duringa sensing operating mode;

FIG. 5 shows an embodiment of a biaxial sensor;

FIG. 6 shows an embodiment of a triaxial sensor; and

FIG. 7 shows a block diagram of a sensor device provided with themicroelectromechanical structure according to a further embodiment ofthe invention.

DETAILED DESCRIPTION

One embodiment of the present invention envisages the provision ofadditional anchorages and elastic anchorage elements connected to thedriving mass 3 in order to improve the stiffness of the same drivingmass 3 for movements outside the plane of the sensor xy.

As shown in FIG. 3 wherein same reference numerals refer to sameelements as those in FIG. 1, the microelectromechanical sensor, heredenoted with 1′, differs from the sensor described with reference toFIG. 1 in that it further comprises a first and a second externalanchorage arrangements 30, 31, coupled to the driving mass 3.

In detail, the first and second external anchorage arrangements 30, 31are positioned externally of the driving mass 3, and are coupled toopposite sides of the same driving mass 3, with respect to the emptyspace 6 and center O; in the exemplary embodiment shown in FIG. 3, thefirst and second external anchorage arrangements 30, 31 are also alignedalong the first axis x, and are diametrically opposite and symmetricwith respect to the empty space 6.

Each of the first and second external anchorage arrangements 30, 31includes a pair of external anchorages 32 (each one coupled to thesubstrate 2, as shown in the following FIG. 4) and a pair of externalelastic anchorage elements 33, coupling a respective external anchorage32 to the driving mass 3. In the exemplary embodiment of FIG. 3, theexternal anchorages 32 and external elastic anchorage elements 33 ofeach pair are arranged on opposite sides of, and symmetrically withrespect to, the first axis x.

Each one of the external elastic anchorage elements 33 comprises afolded spring, generically extending along the first axis x and havingthe shape of a “S-shaped” folded beam. In greater detail, each foldedspring includes: a first arm A, extending along the first axis x andconnected to a respective outer side of the driving mass 3; a second armB extending along the first axis x, parallel to the first arm A, andconnected to a respective external anchorage 32; an intermediate arm C,also extending along the first axis x, and interposed between the firstand second arms A, B in the second direction y; and a first and a secondconnecting portions D, E, extending along the second axis y andconnecting (at a 90° angle) a respective end of the intermediate arm tothe first arm A and to the second arm B, respectively.

Operation of the microelectromechanical sensor 1′ does not differ fromthe one previously discussed with reference to FIG. 1, so that anangular velocity {right arrow over (Ω)}_(x) about the first axis x issensed by the sensor as a function of the displacement of the pair offirst sensing masses 16a, 16b out of the plane of the sensor xy (causedby the Coriolis Force F_(c)) and the associated capacitance variation ofthe detection capacitors.

However, the presence of the additional first and second externalanchorage arrangements 30, 31 improves the overall stiffness of thedriving mass 3 and allows to achieve an improved decoupling of thedriving and sensing modes, particularly avoiding undesired movements ofthe driving mass 3 outside of the plane of the sensor xy.

In other words, and as shown in FIG. 4, when the Coriolis force F_(c)acts on the structure, only the first sensing masses 16a, 16b undergo arotation outside the plane of the sensor xy, while the movement of thedriving mass 3 remains substantially unaltered (and lying in the planeof the sensor xy), so that the sensitivity of the sensor is notaffected. Also, it has been proven that undesired vibration modes of thestructure, that may arise due to the presence of the additionalanchorage elements, are sufficiently removed that they do not interferewith the correct operation of the sensor.

Furthermore, the first and second external anchorage arrangements 30, 31are configured in such a manner that they have a minimum stiffness inthe plane of the sensor xy, and they substantially do not influence thedriving dynamic in the plane of the sensor xy and in particular they donot alter the driving movement of the driving mass 3. Indeed, the foldedspring can be subjected to large movements in the plane of the sensorxy, so that they do not influence the linearity of the system. Also, theApplicant has proven that the residual stresses that could be generateddue to the presence in the structure of different anchoring points tothe substrate 2 are minimized by the disclosed anchorage arrangement (inparticular, due to the minimum stiffness in the plane of the sensor xyof the external anchorage elements 30, 31, the residual stresses, ifpresent, do not influence the driving dynamic).

FIG. 5 shows a biaxial sensor structure according to a furtherembodiment of the present invention.

The microelectromechanical sensor 1′ further includes: a second pair ofthrough-openings 9c, 9d, which are aligned along the second axis y, areof a substantially rectangular shape elongated in a direction parallelto the first axis x, and are arranged on opposite sides with respect tothe empty space 6; and a second pair of acceleration sensors with axisparallel to the orthogonal axis z, and in particular a second pair offirst sensing masses 16c, 16d, housed within the through-openings 9c,9d, and completely enclosed and contained within the driving mass 3. Thefirst sensing masses 16c, 16d are obtained by rotation through 90° ofthe first sensing masses 16a, 16b, and consequently the correspondingelastic supporting elements 20 extend parallel to the first axis x andenable rotation of the respective sensing masses about an axis ofrotation parallel to the first axis x. A second pair of first and seconddetection electrodes 22, 23 is arranged underneath the first sensingmasses 16c, 16d, forming therewith respective detection capacitors. Inuse, the microelectromechanical sensor 1′ is also able to detect anangular velocity {right arrow over (Ω)}_(y) about the second axis y. Therotary motion about the second axis y causes a Coriolis force F_(c),once again directed along the orthogonal axis z, which causes rotationof the first sensing masses 16c, 16d about the axis of rotation parallelto the first axis x, and consequent opposite unbalancing of thedetection capacitors. In particular, a rotation about the first axis xis not sensed by the second pair of first sensing masses 16c, 16d, in sofar as the resultant Coriolis force {right arrow over (F)}_(c) is zero(on account of the fact that the vector product between the angularvelocity {right arrow over (Ω)}_(x) and the corresponding drivingvelocity {right arrow over (v)}_(a) is, at least in a firstapproximation, zero). Likewise, the rotation about the second axis y isnot sensed for similar reasons by the first pair of first sensing masses16a, 16b, and consequently the two axes of detection are not affectedand are decoupled from one another.

A still different embodiment of the present invention envisages amicroelectromechanical structure sensing also angular velocities aboutthe orthogonal axis z (thus operating as a triaxial sensor).

In detail (see FIG. 6), the microelectromechanical sensor 1′ furthercomprises a pair of accelerometers with axis lying in the plane of thesensor xy (for example, with their axis lying at an angle of about 45°with respect to the first and second axes x, y), and in particular apair of second sensing masses 35a, 35b set within a third pair ofthrough-openings 36a, 36b. The through-openings 36a, 36b are rectangularand are aligned in a radial direction (in the example of FIG. 6,inclined of about 45° with respect to the x and y axes) with their mainextension in a direction orthogonal to the radial direction. The secondsensing masses 35a, 35b have a generally rectangular shape with sidesparallel to corresponding sides of the through-openings 36a, 36b, aresuspended with respect to the substrate 2, and are connected to thedriving mass 3 via second elastic supporting elements 38. The secondelastic supporting elements 38 originate from a point situatedapproximately at the center of main sides of the second sensing masses35a, 35b, and extend in the first radial direction. In particular, thesecond elastic supporting elements 38 are rigid with respect to thedriving motion of the driving mass 3, and exclusively enable a movementin the radial direction of the respective second sensing masses, whilehindering movement in other directions (in other words, they arecompliant exclusively in the first radial direction). Furthermore, thesecond sensing masses 35a, 35b have extensions 39 extending from a pointsituated approximately at the centre of corresponding smaller sidesalong the direction orthogonal to the first radial direction. Theextensions 39, together with fixed electrodes anchored to the substrate,facing the extensions 39 and parallel thereto, form detection capacitorswith plane and parallel plates. For example, from each smaller side ofeach second sensing mass 35a, 35b a respective extension 39 originates,facing and set between two fixed electrodes. In a way similar to whathas been previously described, it is possible to denote, as firstdetection electrodes 22, the fixed electrodes arranged in a radiallyouter position, and as second detection electrodes 23 the fixedelectrodes arranged in a radially inner position with respect to thecenter O. Alternatively, a higher number of electrodes can be provided,comb-fingered to one another. In any event, the detection capacitors arein this case in the plane of the sensor xy.

In use, the driving mass 3 is rotated about the orthogonal axis z with adriving angular velocity {right arrow over (Ω)}_(a) (for example,counter-clockwise), dragging along with it the second sensing masses35a, 35b. An external angular velocity {right arrow over (Ω)}_(e) to bedetected, which also acts about the orthogonal axis z, generates aCoriolis force {right arrow over (F)}_(c) on the second sensing masses35a, 35b directed in the radial direction (hence directed as acentrifugal force acting on the same masses), causing displacement ofthe second sensing masses and a capacitive variation of the detectioncapacitors (as discussed in greater detail in the above applicationUS2007/214883).

It is evident that the second sensing masses 35a, 35b can be aligned inany direction of the plane of the sensor xy, the third axis of detectionbeing orthogonal to the plane of the sensor xy and constituting an axisof yaw out of the plane of the sensor xy.

FIG. 7 illustrates a sensor device 40 according to a further embodimentand comprising: the microelectromechanical sensor 1′; a driving circuit41, connected to the driving assembly 4 for imparting the rotary drivingmotion on the driving mass 3; and a read circuit 42, connected to thedetection electrodes 22, 23 for detecting the displacements of thesensing masses. The read circuit 42 is also configured to switch a modeof operation of the microelectromechanical sensor 1′ between a gyroscopemode and an accelerometer mode, by simply modifying the electricalconnections between the sensing masses and the electrodes.

The advantages of the microelectromechanical sensor are clear from theforegoing description.

In particular, adding further external anchorages and elastic anchorageelements (particularly of the folded type) allows to achieve, whennecessary (e.g. when flaws in the manufacturing process occur), animproved decoupling between the driving and sensing modes, andparticularly:

-   -   a reduced interference of the driving arrangement on the sensing        arrangement;    -   a farther separation of the undesired vibration modes away from        the operating frequency range;    -   an improved control of the sensitivity; and    -   an improved resistance to external shocks.

The use of folded springs for the external elastic anchorage elementsallows a greater displacement of the driving mass 3 in the plane of thesensor xy (compared to other type of springs), and minimizes possibledisturbance effects on the linearity of the system.

A correct sizing of the additional external anchorage arrangementsassures the linearity of the sensor and does not introduce any furtherresidual stress in the sensor structure.

Moreover, the microelectromechanical sensor has compact dimensions,given the presence of a single driving mass that encloses in its overalldimensions the sensing masses. The rotary motion of the driving massenables two components of driving velocity, orthogonal to one another inthe plane of the sensor, to be automatically obtained, and henceeffective implementation of a biaxial detection.

Finally, it is clear that modifications and variations can be made towhat is described and illustrated herein, without thereby departing fromthe scope of the present invention.

In particular, a different number and positioning of the externalanchorages and elastic anchorage elements may be provided, as well as adifferent shape and type of the same elastic anchorage elements,different from the folded one (e.g. “L-shaped” elastic elements couldequally be used, or other stress-release elastic elements).

The driving mass 3 can have a shape different from the circular one, forexample any closed polygonal shape. Furthermore, even though this maynot be advantageous, said shape may not have a perfect radial symmetry(or in general any other type of symmetry).

In a per-se known manner, the displacement of the sensing masses can bedetected with a different technique other than the capacitive one, forexample, by detecting a magnetic force.

Furthermore, the torsional moment for causing the driving mass tooscillate with rotary motion can be generated in a different manner, forexample by means of parallel-plate electrodes, or else magneticactuation.

The various embodiments described above can be combined to providefurther embodiments. All of the above U.S. patents, U.S. patentapplication publications, U.S. patent applications, foreign patents,foreign patent applications and non-patent publications referred to inthis specification and/or listed in the Application Data Sheet, areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. An integrated microelectromechanicalstructure, comprising: a substrate; a driving mass designed to be movedwith a rotary motion about an axis of rotation and having a centralaperture relative to a central axis; a first anchorage arrangementpositioned in the central aperture and structured to anchor the drivingmass to the substrate; arranged at the central axis and coupled to thesubstrate; a first opening provided within said driving mass; elasticanchorage elements coupling the driving mass to the first anchorage; afirst sensing mass of a first type arranged inside said first opening;first elastic supporting elements connecting coupling said first sensingmass to said driving mass and configured to enable the first sensingmass to move in a first direction in response to a first acceleration toperform a first detection movementin the presence of a first externalstress; a second sensing mass that is of a type that is different fromthe first sensing mass; second elastic supporting elements coupledbetween the driving mass and the second sensing mass and configured toenable the second sensing mass to perform a second detection movement inresponse to a second acceleration, said first detection movement being arotational movement about a first axis lying in a plane of said drivingmass, and said second detection movement being a linear movement along asecond axis lying in said plane; a second anchorage arrangementpositioned externally of said driving mass and coupled to a first sideof the driving mass; a third anchorage arrangement positioned externallyof said driving mass and coupled to a second side of the driving mass,the second side being opposite to the first side; wherein said firstelastic supporting elements and said first, second and third anchoragearrangements anchorages are so configured so that said driving firstsensing mass is fixed to said first sensing driving mass of the firsttype in said rotary motion and driven relative to the central axis, andthe first sensing mass is decoupled therefrom in said detection movementfrom the driving mass when moving in said first direction.
 2. Thestructure according to claim 1, wherein said driving mass has an annularshape extending substantially in a plane, and said central axis ofrotation is perpendicular to said plane, and said first anchoragearrangement includes: a central anchorage arranged substantially at acenter of said driving mass in the central aperture defined by saidannular shape, and central elastic anchorage elements coupling saidcentral anchorage to said driving mass, extending in said centralaperture; and wherein said second side is opposite to said first side ofthe driving mass with respect to said central aperture axis.
 3. Thestructure according to claim 2 1, wherein said second and thirdanchorage arrangements anchorages are diametrically opposite andsymmetric with respect to said central aperture axis.
 4. The structureaccording to claim 1, wherein each of said second and third anchoragearrangements anchorages comprises an external anchorage member coupledto the substrate, and an external elastic anchorage element couplingsaid external anchorage to said driving mass, extending outside saiddriving mass.
 5. The structure according to claim 4, wherein saidexternal elastic anchorage element comprises a folded spring.
 6. Thestructure according to claim 1, wherein each of said second and thirdanchorage arrangements anchorages comprises a pair of externalanchorages members coupled to the substrate, and a pair of foldedsprings connecting a respective one of said external anchorages membersto said driving mass.
 7. The structure according to claim 1, whereinsaid external stress first acceleration is generated by a Coriolis forceacting in a direction perpendicular to a plane of said driving mass, andsaid first detection movement is a rotation outside said plane about anaxis defined by said first elastic supporting elements.
 8. The structureaccording to claim 1, wherein said driving mass extends substantially ina plane and the structure further comprises: a second sensing mass ofthe first type, which that is aligned with said first sensing mass ofthe first type along a first axis of detection lying in said plane andis arranged in a second opening provided within said driving mass, saidfirst and second sensing masses of the first type being enclosed inoverall dimensions located inward of said driving mass in said plane;and detection means associated with each of said first and secondsensing masses of the first type for detecting said a first detectionmovement, said first detection movement being a rotational movementabout an axis lying in said plane and perpendicular to said first axisof detection.
 9. The structure according to claim 8, wherein saiddetection means are configured to implement a differential detectionscheme.
 10. The structure according to claim 8, wherein said detectionmeans include detection electrodes which are set facing said first andsecond sensing masses of the first type.
 11. The structure according toclaim 1, further comprising: a second sensing mass of the first type,forming with said first sensing mass of the first type a first pair ofsensing masses of the first type aligned along a first axis of detectionlying in a plane on opposite sides with respect to said first anchoragearrangement; and a second pair of sensing masses of the first typealigned along a second axis of detection lying in said plane andorthogonal to said first axis of detection, on opposite sides of saidfirst anchorage arrangement.
 12. The structure according to claim 1,further comprising: a sensing mass of a second type arranged inside asecond opening provided within said driving mass; and second elasticsupporting elements coupled between the driving mass and the sensingmass of the second type and configured to enable the sensing mass of thesecond type to perform a second detection movement in a presence of asecond external stress, said first detection movement being a rotationalmovement about a first axis lying in a plane of said driving mass, andsaid second detection movement being a linear movement along a secondaxis lying in said plane.
 13. The structure according to claim 12 1,wherein said second external stress is acceleration is generated by aCoriolis force acting in a radial direction, and said linear movement isdirected along said radial direction.
 14. The structure according toclaim 12 1, defining a triaxial gyroscope, further including: a secondthird sensing mass of the first type, forming with said first sensingmass of the first type a first pair of sensing masses of the first typealigned along a first axis of detection lying in a plane on oppositesides with respect to said first anchorage arrangement; and a secondpair of sensing masses of the first type aligned along a second axis ofdetection lying in said plane and orthogonal to said first axis ofdetection, on opposite sides of said first anchorage arrangement,wherein said first and second pairs of sensing masses of the first typeare configured to detect, respectively, a first external angularvelocity and a second external angular velocity about said first andsecond axis of detection, and said second sensing mass of the secondtype is configured to detect a third external angular velocity about athird axis of detection orthogonal to said plane.
 15. A sensor devicecomprising: a microelectromechanical structure including: a driving massdesigned to be moved with a rotary motion about an axis of rotation; afirst anchorage positioned along said axis of rotation; first elasticanchorage elements anchoring said driving mass to said first anchorage;a first opening provided within said driving mass; a first sensing massarranged inside said first opening; first elastic supporting elementsconnecting said first sensing mass to said driving mass and configuredto enable said first sensing mass to perform a first detection movementin the presence of an external stress; a second anchorage positionedexternally of said driving mass; and a second elastic anchorage elementcoupling an external side of the driving mass to said second anchorage;wherein said first elastic supporting elements and said first and secondelastic anchorage elements are so configured that said first sensingmass is fixed to said driving mass in said rotary motion, and issubstantially decoupled from said driving mass in said detectionmovement.
 16. The sensor device according to claim 15, furthercomprising a read stage configured to switch a mode of operation of saidmicroelectromechanical structure between a gyroscope mode and anaccelerometer mode.
 17. The sensor device of claim 15, wherein thesecond elastic anchorage element couples a first side of the drivingmass to said second anchorage, the sensor device further comprising: athird anchorage positioned externally of said driving mass; and a thirdelastic anchorage element coupling a second side of the driving mass tosaid third anchorage.
 18. The sensor device according to claim 15,wherein the first sensing mass is of a first type, themicroelectromechanical structure further comprising: a sensing mass of asecond type arranged inside a second opening provided within saiddriving mass; and second elastic supporting elements coupled between thedriving mass and the sensing mass of the second type and configured toenable the sensing mass of the second type to perform a second detectionmovement in a presence of a second external stress, said first detectionmovement being a rotational movement about a first axis, and said seconddetection movement being a linear movement along a second axis.
 19. Thesensor device according to claim 18, defining a triaxial gyroscope, themicroelectromechanical structure further including: a second sensingmass of the first type, forming with said first sensing mass of thefirst type a first pair of sensing masses of the first type alignedalong a first axis of detection on opposite sides with respect to saidfirst anchorage; and a second pair of sensing masses of the first typealigned along a second axis of detection orthogonal to said first axisof detection, on opposite sides of said first anchorage, wherein saidfirst and second pairs of sensing masses of the first type areconfigured to detect, respectively, a first external angular velocityand a second external angular velocity about said first and second axisof detection, and said sensing mass of the second type is configured todetect a third external angular velocity about a third axis of detectionorthogonal to first and second axes of detection.
 20. Amicroelectromechanical device comprising: a first anchorage; firstelastic anchorage elements; a driving mass operable to move in a rotarymotion about an axis of rotation, the driving mass being anchored viathe first elastic anchorage elements to the first anchorage positionedalong the axis of rotation and the driving mass substantially extendingin a plane perpendicular to the axis of rotation; a first openingdisposed positioned within the driving mass; first elastic supportingelements; a first sensing mass of a first type disposed positionedwithin the first opening and having side surfaces enclosed by saiddriving mass, the first sensing mass being coupled to the driving massvia the first elastic supporting elements, the first elastic supportingelements being configured to allow for a first detection movement inresponse to a first external stress, the first detection movement beinga rotational movement outside the plane about an axis lying in theplane; a pair of further second anchorages positioned externally of thedriving mass; furthersecond elastic anchorage elements coupling, each ofthe second elastic anchorage elements being coupled between one of thefurthersecond anchorages to oppositeand external sides of said drivingmass; the first elastic supporting elements and the first and furtherelastic anchorage elements being configured to fix the first sensingmass to the driving mass during said rotary motion, and wherein thefirst and further elastic anchorage elements are being configured toprevent said driving mass from undergoing said rotational movementoutside the plane in response to said first external stress.
 21. Thedevice according to claim 20, further comprising: a second sensing massof the first type, which is aligned with said first sensing mass of thefirst type along a first axis of detection lying in said plane and isarranged in a second opening provided within said driving mass, saidfirst and second sensing masses of the first type being enclosed inoverall dimensions of said driving mass in said plane; and detectionmeans associated with each of said first and second sensing masses ofthe first type for detecting said first detection movement, said firstdetection movement being a rotational movement about an axis lying insaid plane and perpendicular to said first axis of detection.
 22. Thedevice according to claim 20, further comprising a second sensing massof a second type arranged inside a second opening provided within saiddriving mass and connected coupled to said driving mass via secondelastic supporting elements in such a manner so as to perform a seconddetection movement in a presence of a second external stress, said firstdetection movement being a rotational movement about a first axis lyingin said plane, and said second detection movement being a linearmovement along a second axis lying in said plane.
 23. The deviceaccording to claim 22, wherein said second external stress is a Coriolisforce acting in a radial direction, and said linear movement is directedalong said radial direction.
 24. The device according to claim 22,defining a triaxial gyroscope, further including: a second third sensingmass of the first type, forming with said first sensing mass of thefirst type a first pair of sensing masses of the first type alignedalong a first axis of detection lying in a plane on opposite first andsecond sides with respect to said first anchorage; and a second pair ofsensing masses of the first type aligned along a second axis ofdetection lying in said plane and orthogonal to said first axis ofdetection, on opposite third and fourth sides of said first anchorage,wherein said first and second pairs of sensing masses of the first typeare configured to detect, respectively, a first external angularvelocity and a second external angular velocity about said first andsecond axes of detection, and said second sensing mass of the secondtype is configured to detect a third external angular velocity about athird axis of detection orthogonal to said plane.